Embodiments of the present invention generally relate to a method and device for treating a source of hydrogen gas, such as from a reformer, in order to remove potentially deleterious contaminating species, particularly ammonia, which may be co-formed during the reformation process or inadvertently introduced by contaminated feedstocks.
Disclosed is a process for removing small amounts of ammonia from a hydrogen gas stream.
The growth in the world's energy needs brought about by population growth has place a severe strain on the increasing declining stocks of proven reserves of traditional energy resources such as coal petroleum and natural gas. Moreover, geo-political issues such as global warming, said to be the result of fossil fuel combustion in the developed world as well as a drive toward energy independence in this country, are themselves driving an increasing emphasis on the use of environmentally friendly energy sources. Sources such as solar, wind, and geothermal are beginning to replace other energy sources to produce is electricity. However, an alternative to the use of gasoline or similar hydrocarbons to fuel personal automobiles remains elusive.
The conversion of liquid hydrocarbon fuel into hydrogen and carbon dioxide to feed polymer electrolyte membrane (PEM) fuel cells in a compact and energy efficient unit has numerous potential applications. Several examples of these applications include the replacement of batteries in remote sensors, laptop computers, and automobiles, wherein power demands can range from several milliwatts to hundreds of kilowatts. Research groups developing mini- and micro-reforming prototypes are considering a number of approaches. Most approaches have focused on designing miniaturized hydrogen plants that involve a number of individual unit operations (see Pettersson, et al., International Journal of Hydrogen Energy, 2001; 26: p. 243-264; Joensen, et al., Journal of Power Sources, 2002; 105: p. 195-201; de Wild, et al., Catalysis Today, 2000; 60: p. 3-10; and Amphlett, et al., International Journal of Hydrogen Energy, 1996; 21: p. 673-678). Two examples of known processes for producing an optimized hydrogen stream are: 1) partial oxidation at 800-1100° C. and ambient pressure, or 2) direct catalytic steam reforming over Cu/Zn/Al2O3 based catalysts at 250° C. and pressure in the range of 0.1-3.5 MPa. Experiments on Cu/Zn/Al2O3 catalysts have established that the direct steam reforming of methanol in a high steam environment can be rapid, and under certain conditions can lead to a favorable product yield with negligible methane formation (Peppley, et al., Applied Catalysis A, 1999; 79: p. 21-29; Agrell, et al., Journal of Power Sources, 2002; 106: p. 249-257).
Fuel cells are well-known and commonly used to produce electricity by an oxidation/reducing (“redox”) reaction to power electrical apparatus such as apparatus on-board space vehicles. In such fuel cells, a plurality of planar fuel cells are typically arranged in a stack surrounded by an electrically insulating frame structure that defines manifolds for directing flow of reducing, oxidant, coolant and product fluids. Each individual cell generally includes an anode electrode and a cathode electrode separated by an electrolyte. A reactant or reducing fluid such as hydrogen is supplied to the anode electrode, and an oxidant such as oxygen or air is supplied to the cathode electrode. In a cell utilizing a proton exchange membrane (“PEM”) as the electrolyte, the hydrogen electrochemically reacts at a surface of the anode electrode to produce protons and electrons. The electrons are conducted to an external load circuit and then returned to the cathode electrode, while the protons transfer through the electrolyte to the cathode electrode, where they react with the oxidant and electrons to produce water and release thermal energy.
Additionally, it is known that some fuel cells operate on pure hydrogen gas, while others utilize a reformate fuel wherein a hydrogen enriched reducing fluid is formed from any of a variety of hydrocarbon fuels by fuel processing components including, for example, use of known autothermal, steam or partial oxidation reformers. Unfortunately, such reformation of hydrocarbon fuels generates ammonia that moves with the reformate fuel gas reactant stream into the fuel cell where the ammonia dissolves in the water in the electrolyte to become ammonium ions. The ammonia is formed in the reformer by a reaction between hydrogen and nitrogen present in the air that is used in the reforming process or nitrogen added to a peak shaved natural gas. The ammonium ions are then adsorbed by the PEM electrolyte to displace protons within the PEM, thereby decreasing conductivity of the PEM, and hence having a significant negative effect on performance of the fuel cell. Depending upon the temperature of the reformer, composition of any catalyst in the reformer, and nitrogen concentration within the reformer, ammonia formed in the reforming process may range from 1-100 parts-per-million (“ppm”). To efficiently operate a fuel cell power plant on such reformate fuel, the ammonia must be effectively removed from the fuel prior to entry of the fuel into the fuel cells of the plant.
Accordingly, there is a need to develop a fuel treatment system for removing ammonia from hydrogen generating reactors including reformate-produced fuels.